Herpes simplex virus 1 (HSV-1) establishes persistent infections in sensory neurons, from which periodic reactivation can cause herpes simplex keratitis, a sight-threatening recurrent disease of the corneal epithelium. An HSV vaccine to protect against primary infection or to therapeutically enhance antiviral immunity to prevent HSV reactivation and corneal disease is not available. We have found that 1) HSV-1 bearing deletion of the virion host shutoff (vhs) protein stimulates immune responses that protect against primary HSV-1 ocular infection and disease in a mouse model of corneal infection with HSV-1. Vhs mutants also protect against reactivation of latent HSV-1, as demonstrated using a UV-B-induced reactivation model. 2) Replication-defective (ICP8-) virus reduces HSV-1 replication in the cornea and nervous system. 3) An ICP8- /vhs- double mutant virus vaccine stimulates stronger immunity and increases protection compared with ICP8- virus, and therapeutically reduces the frequency of UV-B-induced reactivation and ocular pathology in latently infected mice. We have preliminary evidence that ICP8- HSV encoding murine B7-1 or B7-2 costimulation molecules essential for induction of immune responses stimulate stronger immune responses and protection than the parental ICP8- virus. We hypothesize that expression of a host B7 costimulation molecule by an ICP8-/vhs- vaccine will further augment vaccine immunogenicity, increase its capacity to prevent reactivation of HSV from a latently infected host, and protect against HSV-mediated disease. We further hypothesize that the HSV bacterial artificial chromosome (BAC) technology used to derive the ICP8-/vhs- /B7+ vaccine can be used as a DNA vaccine that will be more stable, safe and effective than virus vaccine. Aim 1: We will engineer an ICP8-/vhs- vaccine prototype HSV-1 strain to encode the murine B7-1 or B7-2 costimulation molecule, and determine the in vivo immunogenicity and prophylactic efficacy of the ICP8-/vhs- /B7+ viruses relative to their ICP8-/vhs- parent. Aim 2: We will determine the in vivo therapeutic effectiveness of the ICP8-/vhs- /B7+ viruses. Aim 3: We will determine immunogenicity, and prophylactic and therapeutic efficacy of ICP8-/vhs- /B7+ HSV BAC as a DNA vaccine versus ICP8-/vhs- /B7+ virus vaccine. [unreadable] [unreadable]